CVE-2018-5255 in EOS
Summary
by MITRE
The Mlag agent in Arista EOS 4.19 before 4.19.4M and 4.20 before 4.20.2F allows remote attackers to cause a denial of service (agent restart) via crafted UDP packets.
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Analysis
by VulDB Data Team • 01/10/2020
The vulnerability identified as CVE-2018-5255 affects the Multi-Chassis Link Aggregation (MLAG) agent within Arista Enterprise Operating System versions prior to specific patches. This issue represents a significant security weakness that enables remote attackers to disrupt network operations through carefully constructed UDP packet payloads. The MLAG functionality is critical for maintaining high availability and redundancy in data center networks, making this vulnerability particularly concerning for enterprise environments that rely on Arista switches for core network infrastructure.
The technical flaw resides in the MLAG agent's insufficient input validation mechanisms when processing incoming UDP packets. Attackers can exploit this weakness by sending malformed or specially crafted UDP packets to the affected switch, which triggers an unexpected behavior in the agent's processing logic. This exploitation results in the MLAG agent crashing and subsequently restarting, causing temporary disruption to the link aggregation functionality. The vulnerability specifically targets the agent's handling of UDP packet headers and payload structures without proper sanitization or boundary checking, creating a condition where malformed data can cause memory corruption or resource exhaustion within the agent process.
The operational impact of this vulnerability extends beyond simple service disruption as it affects the fundamental redundancy mechanisms that network administrators depend upon. When the MLAG agent restarts due to crafted UDP packets, the affected switch loses its ability to maintain aggregated links across multiple chassis, potentially leading to network partitions or temporary service degradation. This disruption can cascade through the network infrastructure, especially in environments where MLAG is used for critical paths between core and distribution switches. The remote nature of the attack means that adversaries do not require physical access or local network privileges, making the vulnerability particularly dangerous in publicly accessible network segments.
Organizations should implement immediate mitigations including applying the vendor patches released for EOS versions 4.19.4M and 4.20.2F, which contain the necessary code modifications to properly validate UDP packet inputs. Network segmentation and access control measures can help limit exposure by restricting which systems can send UDP packets to affected switches. The vulnerability aligns with CWE-129, Input Validation, and CWE-248, Uncaught Exception, as it demonstrates both inadequate validation of input data and failure to properly handle malformed inputs. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, Endpoint Denial of Service, and T1562.001, Impairing Defenses, representing a service disruption attack that targets network infrastructure components. Network monitoring should be enhanced to detect unusual patterns of UDP traffic that might indicate exploitation attempts, and baseline network behavior should be established to quickly identify when MLAG agents are being restarted due to external interference.